1. Field of the Invention
The present invention relates to an apparatus for detecting a position of a substrate, and also relates to an ellipsometer and a film thickness measuring apparatus.
2. Description of the Background Art
Conventionally, when various processings, measurements, or the like are performed on a semiconductor substrate (hereinafter, simply referred to as “substrate”), a relative position of the substrate to a mechanism which is used for the processings or measurements is detected and adjustment of a position or an orientation of the substrate (i.e., adjustment of a rotational position) is performed.
For example, in a pre-aligner disclosed in Japanese Patent Application Laid-Open No. 2004-363218 (Document 1), light is applied from a floodlight lamp positioned above a peripheral portion of an approximately circular wafer to the wafer which rotates around a rotation axis along the vertical direction and light after passing through a notch of the wafer is received by a photodetector positioned below the peripheral portion of the wafer and thereby, a position of the notch of the wafer is detected and the wafer is positioned on the basis of a detection result. In the pre-aligner, even in a case where the peripheral portion of the wafer deviates from a predetermined position due to tolerances of wafer diameter, eccentricity of the wafer on a stage or the like, a notch detecting sensor having the floodlight lamp and the photodetector is linearly moved in a radial direction of the wafer and positioned above the peripheral portion of the wafer, to thereby surely detect the notch of the wafer.
An ellipsometer for measuring a thickness of a film formed on a substrate or the like is used as one of apparatuses for performing optical measurement on a substrate. In the ellipsometer, polarized light is applied to a measurement surface of an object from a light irradiation part so as to incline to the measurement surface, and reflected light of the polarized light is received by a light receiving part, to acquire a polarization state. Ellipsometry of the reflected light is performed to obtain a film thickness on the substrate and a surface state of the measurement surface.
In such an ellipsometer, it is necessary that a relative position of the substrate to the light irradiation part and the light receiving part is accurately adjusted before measurement. Especially, in a case where ellipsometry of a substrate having a fine pattern is performed, higher precision-position detection and position adjustment of the substrate must be performed.
However, like in Document 1, if a mechanism for rotating the stage holding a substrate is provided for position detection of the substrate, the whole apparatus is upsized. Also, with recent upsizing of a substrate, the stage and the mechanism for rotating the stage are further upsized.